This invention relates to the separation of a water-in-oil emulsion into separate water and oil phases. More particularly, the present invention relates to the selection of a demulsifier for use in the separation of such emulsions into water and oil phases.
In oil fields, water usually is produced with crude oil. The complexity of separating mixtures of water and oil depends upon the physical form of the water. Where the mixture has only "free" water, the water will separate readily from the oil because of the differences in gravities of the water and oil. This type of separation presents no problem other than providing a vessel in which water-oil phase separation can occur. However, the water can be dispersed throughout the oil in very minute particles, usually with diameters less than 25 microns. This mixture may be termed a stable emulsion and is very difficult to separate into water and oil phases.
The breaking of stable water-in-oil emulsions may be achieved by physical and chemical treatments, application of heat, and electrical methods, or by a combination of these treatments. In many instances chemical demulsifiers are added to the emulsion to counteract the effects of emulsifiers which provide the stability of the dispersed water particles in the oil phase. There are a magnitude of complex chemical compositions which serve as demulsifiers. Surface-active materials have been used successfully as demulsifiers. The demulsifiers usually have a variety of polar components with a preferred solubility ranging from predominantly oil-soluble to predominantly water-soluble.
The selection of a demulsifier for breaking a particular emulsion has, in the past, been based primarily on trial-and-error procedures. There is, therefore, a real need for a more effective method for determining the performance of demulsifiers in breaking and controlling water-in-oil emulsions.